Tutor profile: Michael P.
Subject: Biomedical Science
What is polymerase chain reaction (PCR)?
Polymerase chain reaction (PCR) is a process used to isolate and copy a specific gene within a genome. The first step of PCR is to identify a target gene and add primers that will bind to that gene. After the addition of primers, the DNA must be denatured (the double helix of DNA will be split into two single helices). This is done by raising the temperature of the environment to about 94C which breaks the hydrogen bonds between the strands. The next step is to "anneal" the DNA, or to lower the temperature to about 50C - this is where the primers will bind to the target gene. The last step is synthesis which occurs at about 72C (because Taq polymerase, the specific DNA polymerase used in PCR, works best at this temperature). Taq polymerase amplify the target gene by adding nucleotides to the 3' end of the primers. This process is repeated 20-30 times to amplify the gene as many times as necessary. The amount of copies increases exponentially with every cycle, so many thousands to millions of copies may be isolated by the end of PCR.
Describe aerobic respiration.
Respiration is an important physiological process that is necessary in all living things. This is the process by which we create energy. There are different ways to create this energy depending on the type of organism or the resources available to the organism. Aerobic respiration is the process of creating energy in the presence of oxygen. While many organisms only use anaerobic respiration (which does not use oxygen), humans, other mammals, and others use primarily aerobic respiration. The first step of respiration is always "glycolysis," which is the breakdown of glucose into two molecules of pyruvate in the cytoplasm of the cell. This does not require oxygen. This process uses 2 ATP molecules but will create 4 ATP molecules, giving us a net gain of 2 ATP molecules. The next two steps require the presence of oxygen, which is why they are only part of aerobic respiration. After glycolysis occurs in the cytoplasm, the two pyruvate molecules will undergo a molecular change and will be transported into the mitochondria of the cell as Acetyl-CoA. This Acetyl-CoA will undergo a molecular change to turn into citric acid which will go through the citric acid cycle (or Krebs Cycle). At the end of the citric acid cycle, we will have created 4 ATP molecules, 6 CO2 molecules, and will have reduced some electron carriers. These electron carriers are important in the next step which is the electron transport chain (ETC). The ETC is a chain of multiple proteins embedded in the inner wall of the mitochondria. The electron carriers just mentioned will "drop off" their electrons at the first protein, and these electrons will travel all the way down the chain to be "picked up" by an oxygen molecule at the end. As the electrons travel, they release energy - this allows the embedded proteins to move protons across the membrane. These protons will be used to power ATP synthase, the protein used to create ATP. At the end of this process, we will create about 30 ATP molecules.
Describe feedback loop that pertains to the regulation of Blood Glucose Level (BGL) in a non-diabetic individual.
The set point for Blood Glucose Level (BGL) is typically 70-110 mg/dL. Before or after a meal, this level can change quite a bit, so we have a way to keep it at a safe level no matter when you ate your last meal. If you haven't eaten in a while (fasting), BGL will decrease. This will be detected by specific cells in the pancreas. These are called $$ \alpha $$ (alpha) cells and they are found in the Islets of Langerhans. When these cells sense that BGL is low, they will secrete a hormone called glucagon. Glucagon will bind to liver cells, which will cause the break down of glycogen (or the stored form of glucose/sugar) to be released into the blood. This will bring BGL back up to its normal level. If you have just eaten a meal, your BGL will increase. The $$ \beta $$ (beta) cells in the Islets of Langerhans will now detect this change and will secrete a hormone called insulin into the bloodstream. Insulin's purpose is to bind to many cells throughout the body - this signal tells these cells that there is plenty of sugar in the blood ready to be used to create energy or to be stored. Body cells will take up this glucose and use it to make ATP, and liver & muscle cells will take up the glucose and store it as glycogen to be used at a later time. This negative feedback loop will make sure we keep BGL at a safe level throughout the day.
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